/****************************************************************************
 *
 * Copyright 2020 Samsung Electronics All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
 * either express or implied. See the License for the specific
 * language governing permissions and limitations under the License.
 *
 ****************************************************************************/
/****************************************************************************
 * lib/libc/stdio/lib_dtoa_engine.c
 *
 *   Copyright © 2018, Keith Packard
 *   All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name NuttX nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <tinyara/math.h>
#include <sys/types.h>

#include "lib_dtoa_engine.h"

/****************************************************************************
 * Pre-processor Definitions
 ****************************************************************************/

/* A bit of CPP trickery -- construct the floating-point value 10 ** DBL_DIG
 * by pasting the value of DBL_DIG onto '1e' to
 */

#define PASTE(a)      1e##a
#define SUBSTITUTE(a) PASTE(a)
#define MIN_MANT      (SUBSTITUTE(DBL_DIG))
#define MAX_MANT      (10.0 * MIN_MANT)
#define MIN_MANT_INT  ((uint64_t)MIN_MANT)
#define MIN_MANT_EXP  DBL_DIG

#define MAX(a, b)     ((a) > (b) ? (a) : (b))
#define MIN(a, b)     ((a) < (b) ? (a) : (b))

/****************************************************************************
 * Public Functions
 ****************************************************************************/

int __dtoa_engine(double_t x, FAR struct dtoa_s *dtoa, int max_digits, int max_decimals)
{
	int32_t exp = 0;
	uint8_t flags = 0;
	int i;

	if (__builtin_signbit(x)) {
		flags |= DTOA_MINUS;
		x = -x;
	}

	if (x == 0) {
		flags |= DTOA_ZERO;
		for (i = 0; i < max_digits; i++) {
			dtoa->digits[i] = '0';
		}
	} else if (isnan(x)) {
		flags |= DTOA_NAN;
	} else if (isinf(x)) {
		flags |= DTOA_INF;
	} else {
		double_t y;

		exp = MIN_MANT_EXP;

		/* Bring x within range MIN_MANT <= x < MAX_MANT while computing
		 * exponent value
		 */

		if (x < MIN_MANT) {
			for (i = DTOA_SCALE_UP_NUM - 1; i >= 0; i--) {
				y = x * g_dtoa_scale_up[i];
				if (y < MAX_MANT) {
					x = y;
					exp -= (1 << i);
				}
			}
		} else {
			for (i = DTOA_SCALE_DOWN_NUM - 1; i >= 0; i--) {
				y = x * g_dtoa_scale_down[i];
				if (y >= MIN_MANT) {
					x = y;
					exp += (1 << i);
				}
			}
		}

		/* If limiting decimals, then limit the max digits to no more than the
		 * number of digits left of the decimal plus the number of digits right
		 * of the decimal
		 */

		if (max_decimals != 0) {
			max_digits = MIN(max_digits, max_decimals + MAX(exp + 1, 1));
		}

		/* Round nearest by adding 1/2 of the last digit before converting to
		 * int. Check for overflow and adjust mantissa and exponent values
		 */

		x = x + g_dtoa_round[max_digits];

		if (x >= MAX_MANT) {
			x /= 10.0;
			exp++;
		}

		/* Now convert mantissa to decimal. */

		uint64_t mant = (uint64_t) x;
		uint64_t decimal = MIN_MANT_INT;

		/* Compute digits */

		for (i = 0; i < max_digits; i++) {
			dtoa->digits[i] = mant / decimal + '0';
			mant %= decimal;
			decimal /= 10;
		}
	}

	dtoa->digits[max_digits] = '\0';
	dtoa->flags = flags;
	dtoa->exp = exp;
	return max_digits;
}
